Method for using an iron-based lithium supplement for lithium-ion batteries

Abstract

The present invention provides a method for using an iron-based lithium supplement for a lithium-ion battery. The method comprises the following steps: mixing a positive electrode active material, an iron-based lithium supplement, a conductive agent, a binder, and an organic solvent to obtain a positive electrode slurry; then coating the positive electrode slurry on a current collector and drying the mixture to obtain a positive electrode sheet; assembling the positive electrode sheet, a negative electrode sheet, and a separator, and injecting electrolyte to obtain a liquid-injected battery cell; first sealing the liquid-injected battery cell with a forming nail, then performing formation, pulling out the forming nail after primary aging to perform primary exhaust, then re-sealing with the forming nail, then performing volume separation, and pulling out the forming nail after secondary aging to perform secondary exhaust. This method not only effectively reduces the gas production of the iron-based lithium supplement during the battery cell aging process and improves the gram capacity of the iron-based lithium supplement, but also is compatible with existing production processes and can effectively improve the electrochemical performance of lithium batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a method for using an iron-based lithium supplement for lithium-ion batteries. Background Art

[0002] At present, lithium manganese iron phosphate is a new type of positive electrode material. With the increasing requirements in the process of commercial application, the problems of gram capacity utilization and cycle capacity retention need to be solved urgently. The positive electrode lithium replenishment technology currently adopts the method of adding lithium replenishers to the positive electrode material. The lithium replenisher material decomposes and releases active lithium during the battery charging process to compensate for the irreversible active lithium loss caused by the growth of SEI in the negative electrode, thereby improving the problem of the reduction of the first coulomb efficiency and improving the capacity, cycle life and energy density of the lithium battery. Therefore, the current industrial production of battery cells requires lithium replenishers with stable chemical properties, easy synthesis, low price and high gram capacity utilization, while being compatible with the battery manufacturing process. There is little exploration related to the selection and application of lithium replenishers in the lithium manganese iron phosphate system, which has high research value.

[0003] Lithium-rich ferrite (LFO), with the chemical formula Li5FeO4, is a lithium metal oxide with an inverse fluorite structure. It has a very high specific capacity, with a theoretical gram capacity of up to 867mAh / g, making it an ideal pre-lithium additive. However, LFO will produce a large amount of gas during the aging process of the battery cell, and the generation of gas will affect the battery's cycle and high-temperature performance.

[0004] Therefore, how to effectively reduce the gas production of lithium supplements during the aging process of battery cells and improve the electrochemical performance of batteries is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] In response to the shortcomings of the prior art, the present invention aims to provide a method for using an iron-based lithium supplement for lithium-ion batteries. This method effectively reduces gassing during battery cell aging, solves the problem of gassing and swelling of off-line batteries during use, and improves the specific capacity of the iron-based lithium supplement. Furthermore, this method is compatible with current production processes and can effectively improve lithium battery performance, including capacity, cycle life, and energy density.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for using an iron-based lithium supplement for a lithium-ion battery, the method comprising the following steps:

[0008] (1) mixing a positive electrode active material, an iron-based lithium supplement agent, a conductive agent, a binder, and an organic solvent to obtain a positive electrode slurry, then coating the positive electrode slurry on a current collector, and drying to obtain a positive electrode sheet;

[0009] (2) Assembling the positive electrode sheet, the negative electrode sheet and the separator, and filling the electrolyte to obtain a liquid-filled battery cell;

[0010] (3) The liquid-filled battery cell is first sealed with a forming nail, then formed, and after the first aging, the forming nail is pulled out to perform a first venting, and then the forming nail is used for a second sealing, and then the volume is divided, and after the second aging, the forming nail is pulled out to perform a second venting.

[0011] The present invention designs a method for using an iron-based lithium supplement for lithium-ion batteries, which not only effectively reduces the gas production of the iron-based lithium supplement during the aging process of the battery cells, solves the problem of gas production and swelling of the battery cells offline during use of the iron-based lithium supplement, and improves the gram capacity of the iron-based lithium supplement, but also the method is compatible with the current production process and can effectively improve the performance of the lithium battery, such as the capacity, cycle life and energy density.

[0012] It should be noted that the present invention does not limit the type of conductive agent, and illustratively, it can be carbon nanotubes or VGCF (vapor-grown carbon fiber); the present invention does not limit the type of binder, and illustratively, it can be PVDF (polyvinylidene fluoride); the present invention does not limit the type of organic solvent, and illustratively, it can be N-methylpyrrolidone.

[0013] Preferably, the negative electrode material in the negative electrode plate includes graphite.

[0014] Preferably, the conductive agent in the negative electrode plate includes any one of SP (conductive carbon black), carbon nanotubes or VGCF, or a combination of at least two of them.

[0015] Preferably, the binder in the negative electrode plate includes CMC (sodium carboxymethyl cellulose) or PAA (polyacrylic acid).

[0016] It should be noted that the present invention does not limit the type of the separator. For example, it can be a polypropylene film.

[0017] It should be noted that the present invention does not limit the composition of the electrolyte. For example, the electrolyte can use LiPF6 as the electrolyte, the electrolyte concentration is 1 mol / L, and a mixture of ethylene carbonate and diethyl carbonate with a volume ratio of 1:1 as the solvent.

[0018] As a preferred technical solution of the present invention, the positive electrode active material in step (1) includes lithium manganese iron phosphate.

[0019] Preferably, the iron-based lithium supplement comprises lithium-rich ferric acid (LFO).

[0020] Preferably, in the positive electrode slurry of step (1), the mass content of the iron-based lithium supplement agent is 1-5%, for example, it can be 1%, 2%, 3%, 4% or 5%, and is preferably 3.5-4.5%.

[0021] In the present invention, the mass content of the iron-based lithium supplement is preferably 3.5-4.5%, which can better improve the gram capacity of the main material and the capacity retention rate at high temperature and high rate.

[0022] As a preferred technical solution of the present invention, the specific steps of the chemical formation in step (3) include:

[0023] The sealed liquid-filled battery cell is first left to rest once, then charged with constant current, and then left to rest twice. After that, it is charged with constant current and constant voltage, and left to rest three times.

[0024] As a preferred technical solution of the present invention, the first standing time, the second standing time and the third standing time are independently 8-12 minutes, for example, 8 minutes, 9 minutes, 10 minutes, 11 minutes or 12 minutes.

[0025] Preferably, the constant current charging current is 0.05-0.1C, for example, it can be 0.05C, 0.06C, 0.07C, 0.08C, 0.09C or 0.1C.

[0026] Preferably, the constant current charging time is 60-120 min, for example, 60 min, 80 min, 100 min or 120 min.

[0027] As a preferred technical solution of the present invention, the current of the constant current and constant voltage charging is 0.05-0.1C, for example, it can be 0.05C, 0.06C, 0.07C, 0.08C, 0.09C or 0.1C.

[0028] Preferably, the cut-off voltage of the constant current constant voltage charging is 4.2-4.5V, for example, 4.2V, 4.3V, 4.4V or 4.5V, and the cut-off current is 0.03-0.08C, for example, 0.03C, 0.04C, 0.05C, 0.06C, 0.07C or 0.08C.

[0029] Preferably, the primary aging temperature is 40-60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C, and the primary aging time is 48-72h, for example, 48h, 54h, 60h, 66h or 72h.

[0030] As a preferred technical solution of the present invention, the specific steps of volume separation in step (3) include:

[0031] (a) Perform one resting period, then a constant current discharge, followed by a second resting period;

[0032] (b) constant current and constant voltage charging, followed by three rest periods and then constant current discharge;

[0033] (c) After repeating step (b) 3-5 times, constant current charging is performed, followed by four resting times.

[0034] As a preferred technical solution of the present invention, the first standing time, the second standing time, the third standing time and the fourth standing time independently include 8-12 minutes, for example, they can be 8 minutes, 9 minutes, 10 minutes, 11 minutes or 12 minutes.

[0035] Preferably, the constant current discharge in step (a) is 0.08-0.12C, for example, 0.08C, 0.09C, 0.1C, 0.11C or 0.12C.

[0036] Preferably, the cut-off voltage of the constant current discharge in step (a) is 1.8-2.2V, for example, it can be 1.8V, 1.9V, 2V, 2.1V or 2.2V.

[0037] As a preferred technical solution of the present invention, the current of the constant current and constant voltage charging in step (b) is 0.2-0.5C, for example, it can be 0.2C, 0.3C, 0.4C or 0.5C, preferably 0.25-0.4C, and more preferably 0.3-0.35C.

[0038] Preferably, the cut-off voltage of the constant-current constant-voltage charging in step (b) is 4-4.5V, for example, it can be 4V, 4.1V, 4.2V, 4.3V, 4.4V or 4.5V.

[0039] Preferably, the constant current discharge in step (b) is 0.2-0.5C, for example, 0.2C, 0.3C, 0.4C or 0.5C.

[0040] Preferably, the cut-off voltage of the constant current discharge in step (b) is 2.2-2.8V, for example, it can be 2.2V, 2.3V, 2.4V, 2.5V, 2.6V, 2.7V or 2.8V.

[0041] As a preferred technical solution of the present invention, the constant current charging current in step (c) is 0.3-0.35C, for example, it can be 0.3C, 0.31C, 0.32C, 0.33C, 0.34C or 0.35C.

[0042] Preferably, the constant current charging time in step (c) is 40-80 min, for example, 40 min, 50 min, 60 min, 70 min or 80 min.

[0043] Preferably, the secondary aging temperature is 40-60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C, and the secondary aging time is 48-72h, for example, 48h, 54h, 60h, 66h or 72h.

[0044] As a preferred technical solution of the present invention, the method of use comprises the following steps:

[0045] (1) mixing lithium manganese iron phosphate, lithium-rich ferric acid, carbon nanotubes, a binder, and an organic solvent to obtain a positive electrode slurry, then coating the positive electrode slurry on an aluminum foil, and drying to obtain a positive electrode sheet;

[0046] The mass content of lithium-rich ferric acid in the positive electrode slurry is 1-5%;

[0047] (2) Assembling the positive electrode sheet, the negative electrode sheet and the separator, and filling the electrolyte to obtain a liquid-filled battery cell;

[0048] (3) The liquid-filled battery cell is first sealed by forming nails and then formed. The specific steps of the forming include:

[0049] The sealed liquid-filled battery cell is first rested for 8-12 minutes, then charged at a constant current of 0.05-0.1C for 60-120 minutes, followed by a second rest for 8-12 minutes, and then charged at a constant current and constant voltage of 0.05-0.1C to 4.2-4.5V, with a cut-off current of 0.03-0.08C, followed by a third rest of 8-12 minutes;

[0050] (4) After the formation is completed, the nails are aged at 40-60°C for 48-72 hours, and then the nails are pulled out for exhaust;

[0051] (5) The liquid-filled battery cell treated in step (4) is sealed again using a forming nail, and then the capacity is divided. The specific steps of the capacity division include:

[0052] (a) A rest period of 8-12 minutes, followed by a discharge at a constant current of 0.08-0.12C to a value of 1.8-2.2V, followed by a second rest period of 8-12 minutes;

[0053] (b) charging at a constant current and constant voltage of 0.2-0.5C to 4-4.5V, followed by three rest periods of 8-12min, and then discharging at a constant current of 0.2-0.5C to a cut-off voltage of 2.2-2.8V;

[0054] (c) After repeating step (b) 3-5 times, charge at a constant current of 0.3-0.35C for 40-80 minutes, followed by four resting times of 8-12 minutes;

[0055] (6) After the separation is completed, age at 40-60℃ for 48-72h, then pull out the nails for secondary exhaust.

[0056] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] (1) The present invention designs a method for using an iron-based lithium supplement for lithium-ion batteries, which not only effectively reduces the gas production of the iron-based lithium supplement during the aging process of the battery cell and improves the gram capacity of the iron-based lithium supplement, but also the method is compatible with the current production process and can effectively improve the performance of lithium batteries such as capacity, cycle life and energy density.

[0059] (2) Based on the usage method provided by the present invention, the gram capacity of the iron-based lithium supplement can reach 570 mAh / g, which solves the problem of gas generation and swelling of the offline battery cells during the application of the iron-based lithium supplement, and the offline battery cells have a good appearance.

[0060] (3) Based on the usage method provided by the present invention, the gram capacity of the positive electrode active material can be increased to 143.5 mAh / g. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 The figures are the cycling performance and DCR comparison curves of the lithium-ion batteries prepared in Example 1 and Comparative Example 5 at 25°C.

[0062] Figure 2 Comparative curves of the cycle performance and DCR at 45° C. of the lithium-ion batteries prepared in Example 1 and Comparative Example 5 of the present invention, respectively. DETAILED DESCRIPTION

[0063] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0064] Example 1

[0065] This embodiment provides a method for using an iron-based lithium supplement for lithium-ion batteries, the method comprising the following steps:

[0066] (1) mixing lithium manganese iron phosphate, lithium-rich ferric acid, carbon nanotubes, polyvinylidene fluoride, and N-methylpyrrolidone to obtain a positive electrode slurry, then coating the positive electrode slurry on aluminum foil, and drying to obtain a positive electrode sheet;

[0067] The mass content of lithium-rich ferric acid in the positive electrode slurry is 4%, and the mass ratio of lithium manganese iron phosphate, lithium-rich ferric acid, carbon nanotubes and polyvinylidene fluoride is 93.5:4:0.8:1.7;

[0068] (2) Mixing the negative electrode active material graphite, the conductive agent SP, the binder CMC and the solvent water to obtain a negative electrode slurry, then coating the negative electrode slurry on a copper foil, and drying to obtain a negative electrode sheet;

[0069] (3) Assembling the positive electrode sheet, the negative electrode sheet and the coated polypropylene separator, and injecting the electrolyte (using LiPF6 as the electrolyte, the electrolyte concentration is 1 mol / L, and a mixture of ethylene carbonate and diethyl carbonate with a volume ratio of 1:1 as the solvent) to obtain a liquid-injected battery cell;

[0070] (4) The liquid-filled battery cell is first sealed by forming nails and then formed. The specific steps of the forming include:

[0071] The sealed liquid-filled battery cell was first rested for 10 minutes, then charged at a constant current of 0.08C for 90 minutes, followed by a second rest for 10 minutes, and then charged at a constant current and constant voltage of 0.08C to 4.35V, with a cut-off current of 0.05C, followed by a third rest of 10 minutes;

[0072] (5) After the formation is completed, the nails are aged at 50°C for 60 hours, and then the nails are pulled out for exhaust.

[0073] (6) The liquid-filled battery cell treated in step (5) is sealed again using a forming nail, and then the capacity is divided. The specific steps of the capacity division include:

[0074] (a) A 10-min rest period was followed by a 0.1 C constant current discharge to 2 V, followed by a 10-min rest period.

[0075] (b) Charge at 0.35C constant current and constant voltage to 4.25V, then rest for three 10-min intervals, and then discharge at 0.35C constant current with a cutoff voltage of 2.5V.

[0076] (c) After repeating step (b) four times, the battery was charged at a constant current of 0.32 C for 60 min, followed by four rest periods of 10 min;

[0077] (7) After the separation, the mixture was aged at 50°C for 60 hours, and then the formed nails were pulled out for secondary exhaust.

[0078] Example 2

[0079] This embodiment provides a method for using an iron-based lithium supplement for lithium-ion batteries, the method comprising the following steps:

[0080] (1) mixing lithium manganese iron phosphate, lithium-rich ferric acid, carbon nanotubes, polyvinylidene fluoride, and N-methylpyrrolidone to obtain a positive electrode slurry, then coating the positive electrode slurry on aluminum foil, and drying to obtain a positive electrode sheet;

[0081] The mass content of lithium-rich ferric acid in the positive electrode slurry is 3.5%, and the mass ratio of lithium manganese iron phosphate, lithium-rich ferric acid, carbon nanotubes and polyvinylidene fluoride is 94:3.5:0.8:1.7.

[0082] (2) mixing the negative electrode active material graphite, the conductive agent VGCF, the binder CMC and the solvent water to obtain a negative electrode slurry, then coating the negative electrode slurry on a copper foil, and drying to obtain a negative electrode sheet;

[0083] (3) Assembling the positive electrode sheet, the negative electrode sheet and the coated polypropylene separator, and injecting the electrolyte (using LiPF6 as the electrolyte, the electrolyte concentration is 1 mol / L, and a mixture of ethylene carbonate and diethyl carbonate with a volume ratio of 1:1 as the solvent) to obtain a liquid-injected battery cell;

[0084] (4) The liquid-filled battery cell is first sealed by forming nails and then formed. The specific steps of the forming include:

[0085] The sealed liquid-filled battery cell was first rested for 10 minutes, then charged at a constant current of 0.05C for 120 minutes, followed by a second rest for 10 minutes, and then charged at a constant current and constant voltage of 0.05C to 4.2V, with a cut-off current of 0.03C, followed by a third rest of 10 minutes;

[0086] (5) After the formation is completed, the nails are aged at 40°C for 72 hours, and then the nails are pulled out for exhaust.

[0087] (6) The liquid-filled battery cell treated in step (5) is sealed again using a forming nail, and then the capacity is divided. The specific steps of the capacity division include:

[0088] (a) A 10-min rest period was followed by a 0.08 C constant current discharge to 2.2 V, followed by a 10-min rest period.

[0089] (b) Charge at 0.2C constant current and constant voltage to 4V, then rest for three 10-min periods, and then discharge at 0.2C constant current with a cutoff voltage of 2.2V.

[0090] (c) After repeating step (b) three times, the battery was charged at a constant current of 0.3 C for 80 min, followed by four rest periods of 10 min;

[0091] (7) After the separation, the mixture was aged at 40°C for 72 hours, and then the formed nails were pulled out for secondary exhaust.

[0092] Example 3

[0093] This embodiment provides a method for using an iron-based lithium supplement for lithium-ion batteries, the method comprising the following steps:

[0094] (1) mixing lithium manganese iron phosphate, lithium-rich ferric acid, carbon nanotubes, polyvinylidene fluoride, and N-methylpyrrolidone to obtain a positive electrode slurry, then coating the positive electrode slurry on aluminum foil, and drying to obtain a positive electrode sheet;

[0095] The mass content of lithium-rich ferric acid in the positive electrode slurry is 4.5%, and the mass ratio of lithium manganese iron phosphate, lithium-rich ferric acid, carbon nanotubes and polyvinylidene fluoride is 93:4.5:0.8:1.7;

[0096] (2) mixing graphite, a negative electrode active material, a conductive agent (SP and carbon nanotubes in a mass ratio of 1:1), a binder PAA, and solvent water to obtain a negative electrode slurry, then coating the negative electrode slurry on a copper foil, and drying to obtain a negative electrode sheet;

[0097] (3) Assembling the positive electrode sheet, the negative electrode sheet and the coated polypropylene separator, and injecting the electrolyte (using LiPF6 as the electrolyte, the electrolyte concentration is 1 mol / L, and a mixture of ethylene carbonate and diethyl carbonate with a volume ratio of 1:1 as the solvent) to obtain a liquid-injected battery cell;

[0098] (4) The liquid-filled battery cell is first sealed by forming nails and then formed. The specific steps of the forming include:

[0099] The sealed liquid-filled battery cell is first rested for 8-12 minutes, then charged at a constant current of 0.1C for 60 minutes, followed by a second rest for 8-12 minutes, and then charged at a constant current and constant voltage of 0.1C to 4.5V, with a cut-off current of 0.08C, followed by a third rest for 8-12 minutes;

[0100] (5) After the formation is completed, the nails are aged at 60°C for 48 hours, and then the nails are pulled out for exhaust.

[0101] (6) The liquid-filled battery cell treated in step (4) is sealed again using a forming nail, and then the capacity is divided. The specific steps of the capacity division include:

[0102] (a) A 10-min rest period was followed by a 0.12 C constant current discharge to 1.8 V, followed by a 10-min rest period.

[0103] (b) Charge at 0.5C constant current and constant voltage to 4.5V, then rest for three 10-min periods, and then discharge at 0.5C constant current with a cutoff voltage of 2.8V.

[0104] (c) After repeating step (b) five times, the battery was charged at a constant current of 0.35 C for 40 min, followed by four rest periods of 10 min;

[0105] (7) After the separation, the mixture was aged at 60°C for 48 hours, and then the formed nails were pulled out for secondary exhaust.

[0106] Example 4

[0107] The difference between this embodiment and embodiment 1 is that the current of the constant current discharge in step (a) is 0.05C.

[0108] The rest of the preparation methods and parameters remained the same as in Example 1.

[0109] Example 5

[0110] The difference between this embodiment and embodiment 1 is that the current of the constant current discharge in step (a) is 0.15C.

[0111] The rest of the preparation methods and parameters remained the same as in Example 1.

[0112] Example 6

[0113] The difference between this embodiment and embodiment 1 is that the current of the constant current charging in step (c) is 0.25C.

[0114] The rest of the preparation methods and parameters remained the same as in Example 1.

[0115] Example 7

[0116] The difference between this embodiment and embodiment 1 is that the current of the constant current charging in step (c) is 0.4C.

[0117] The rest of the preparation methods and parameters remained the same as in Example 1.

[0118] Comparative Example 1

[0119] The difference between this comparative example and Example 1 is that the one-time sealing of the nail formation is not performed in step (4).

[0120] The rest of the preparation methods and parameters remained the same as in Example 1.

[0121] Comparative Example 2

[0122] The difference between this comparative example and Example 1 is that no exhaust is performed in step (5).

[0123] The rest of the preparation methods and parameters remained the same as in Example 1.

[0124] Comparative Example 3

[0125] The difference between this comparative example and Example 1 is that no secondary sealing of the formed nails is performed in step (6).

[0126] The rest of the preparation methods and parameters remained the same as in Example 1.

[0127] Comparative Example 4

[0128] The difference between this comparative example and Example 1 is that no secondary exhaust of the formed nails is performed in step (7).

[0129] The rest of the preparation methods and parameters remained the same as in Example 1.

[0130] Comparative Example 5

[0131] The difference between this comparative example and Example 1 is that lithium-rich ferric acid is not added in step (1).

[0132] The rest of the preparation methods and parameters remained the same as in Example 1.

[0133] Figure 1 The cycling performance and DCR comparison curves of the lithium-ion batteries prepared in Example 1 and Comparative Example 5 at 25°C are shown. As can be seen from the figure, the addition of LFO lithium supplement can effectively improve the capacity retention rate and reduce the DCR growth rate, and the lithium-ion battery with the addition of LFO lithium supplement has the advantage of capacity climbing.

[0134] Figure 2 The cycling performance and DCR comparison curves of the lithium-ion batteries prepared in Example 1 and Comparative Example 5 at 45°C are shown. As can be seen from the figure, the addition of LFO lithium supplement can significantly improve the capacity retention rate in a high temperature environment and increase the SOH level by ≥80% for 1000 cycles.

[0135] Performance Testing

[0136] The lithium-ion batteries obtained in the above examples and comparative examples were subjected to electrochemical performance tests, including capacity performance and cycle performance.

[0137] The test conditions for capacity performance are: 25℃, 0.33C / 0.33C.

[0138] The test conditions for the cycle performance are: 25°C, 1C / 1C, 1000 cycles.

[0139] DCR test: 50% SOC 1C30s.

[0140] The test results are shown in Table 1.

[0141] Table 1

[0142]

[0143] analyze:

[0144] As can be seen from the above table, the present invention, by designing a method for using an iron-based lithium supplement for lithium-ion batteries, not only effectively reduces the gas production of the iron-based lithium supplement during the aging process of the battery cell and improves the gram capacity of the iron-based lithium supplement, but also the method is compatible with the current production process, which can effectively improve the performance of lithium batteries such as capacity, cycle life and energy density. The gram capacity of the positive electrode active material can be increased to 143.5 mAh / g.

[0145] It can be seen from Examples 1 and 4-5 that if the current of the constant current discharge in step (a) is too small, the formation time will be too long, and other side reactions will occur, affecting the electrochemical process; if the current of the constant current discharge in step (a) is too large, the gas production will be insufficient, affecting the subsequent exhaust process, and the interface of the offline battery cell electrode will be poor.

[0146] It can be seen from Examples 1 and 6-7 that if the constant current charging current in step (c) is too small, it will affect the formation time and change the Li + The removal process affects the gram capacity; if the current of the constant current charging in step (c) is too large, the gas production will be insufficient, affecting the exhaust process and the offline interface.

[0147] It can be seen from Example 1 and Comparative Examples 1 and 3 that if the primary sealing of the forming nail is not performed, the gas production will be insufficient, and the subsequent gas production of the battery cells after capacity division and offline will be serious, affecting the performance; if the secondary sealing of the forming nail is not performed, the gas production will be insufficient, and the battery cells will produce gas after offline, affecting the performance.

[0148] It can be seen from Example 1 and Comparative Examples 2 and 4 that if the first exhaust is not performed, the battery cell will produce serious gas, the capacity separation process will have a safety hazard, and the offline battery cell disassembly interface will be very poor, the addition of LFO lithium replenisher will not work, and negative gain will occur; if the second exhaust is not performed, the offline battery cell will produce serious gas during the test process, the battery cell disassembly interface will be poor, the LFO lithium replenisher will not work, and negative gain will occur.

[0149] It can be seen from Example 1 and Comparative Example 5 that if lithium-rich ferric acid is not added, the capacity performance and cycle performance of the lithium-ion battery will deteriorate.

[0150] The applicant states that while the above-described embodiments illustrate the process of the present invention, the present invention is not limited to the above-described process steps, nor does it imply that the present invention must rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for using an iron-based lithium supplement for lithium-ion batteries, characterized in that: The method of use comprises the following steps: (1) A positive electrode active material, an iron-based lithium supplement agent, a conductive agent, a binder, and an organic solvent are mixed to obtain a positive electrode slurry, and the positive electrode slurry is then coated on a current collector and dried to obtain a positive electrode sheet; the iron-based lithium supplement agent includes lithium-rich ferric acid; (2) Assembling the positive electrode sheet, the negative electrode sheet and the separator, and filling the electrolyte to obtain a liquid-filled battery cell; (3) The liquid-filled battery cell is first sealed with a forming nail, then formed, and after the first aging, the forming nail is pulled out to perform a first exhaust, and then the forming nail is used for a second sealing, and then the volume is divided, and after the second aging, the forming nail is pulled out to perform a second exhaust; The specific steps of the capacity division in step (3) include: (a) One rest period, followed by a constant current discharge, followed by a second rest period; (b) Constant current and constant voltage charging, followed by three rest periods, and then constant current discharge; (c) After repeating step (b) 3-5 times, constant current charging is performed, followed by four resting steps; The constant current discharge in step (a) is 0.08-0.12C; The constant current charging current in step (c) is 0.3-0.35C.

2. The method of use according to claim 1, characterized in that: The positive electrode active material in step (1) includes lithium manganese iron phosphate.

3. The method of use according to claim 1, wherein: In the positive electrode slurry of step (1), the mass content of the iron-based lithium supplement agent is 1-5%.

4. The method of use according to claim 3, characterized in that: In the positive electrode slurry of step (1), the mass content of the iron-based lithium supplement agent is 3.5-4.5%.

5. The method of use according to claim 1, characterized in that: The specific steps of the formation in step (3) include: The sealed liquid-filled battery cell is first left to rest once, then charged with constant current, and then left to rest twice. After that, it is charged with constant current and constant voltage, and left to rest three times.

6. The method of use according to claim 5, characterized in that: The first standing time, the second standing time and the third standing time are independently 8-12 minutes.

7. The method of use according to claim 5, characterized in that: The constant current charging current is 0.05-0.1C.

8. The method of use according to claim 5, characterized in that: The constant current charging time is 60-120 minutes.

9. The method of use according to claim 5, characterized in that: The current of the constant current constant voltage charging is 0.05-0.1C.

10. The method of use according to claim 5, characterized in that: The cut-off voltage of the constant current and constant voltage charging is 4.2-4.5V, and the cut-off current is 0.03-0.08C.

11. The method of use according to claim 1, characterized in that: The temperature of the primary aging is 40-60° C., and the time of the primary aging is 48-72 hours.

12. The method of use according to claim 1, characterized in that: The first standing time, the second standing time, the third standing time and the fourth standing time are independently 8-12 minutes.

13. The method of use according to claim 1, wherein: The cut-off voltage of the constant current discharge in step (a) is 1.8-2.2V.

14. The method of use according to claim 1, characterized in that: The current of the constant current and constant voltage charging in step (b) is 0.2-0.5C.

15. The method of use according to claim 14, characterized in that: The current of the constant current and constant voltage charging in step (b) is 0.25-0.4C.

16. The method of use according to claim 15, characterized in that: The current of the constant current and constant voltage charging in step (b) is 0.3-0.35C.

17. The method of use according to claim 1, wherein: The cut-off voltage of the constant current and constant voltage charging in step (b) is 4-4.5V.

18. The method of use according to claim 1, characterized in that: The constant current discharge in step (b) is 0.2-0.5C.

19. The method of use according to claim 1, wherein: The cut-off voltage of the constant current discharge in step (b) is 2.2-2.8V.

20. The method of use according to claim 1, wherein: The constant current charging time in step (c) is 40-80 minutes.

21. The method of use according to claim 1, characterized in that: The secondary aging temperature is 40-60° C., and the secondary aging time is 48-72 hours.

22. The method of use according to claim 1, characterized in that: The method of use comprises the following steps: (1) mixing lithium manganese iron phosphate, lithium-rich ferric acid, carbon nanotubes, a binder, and an organic solvent to obtain a positive electrode slurry, then coating the positive electrode slurry on an aluminum foil, and drying to obtain a positive electrode sheet; Among them, the mass content of lithium-rich ferric acid in the positive electrode slurry is 1-5%; (2) Assembling the positive electrode sheet, the negative electrode sheet and the separator, and filling the electrolyte to obtain a liquid-filled battery cell; (3) The liquid-filled battery cell is first sealed by forming nails and then formed. The specific steps of the forming include: The sealed liquid-filled battery cell is first rested for 8-12 minutes, then charged at a constant current of 0.05-0.1C for 60-120 minutes, followed by a second rest for 8-12 minutes, and then charged at a constant current and constant voltage of 0.05-0.1C to 4.2-4.5V, with a cut-off current of 0.03-0.08C, followed by a third rest of 8-12 minutes; (4) After the formation is completed, the nails are aged at 40-60 ° C for 48-72 hours, and then the nails are pulled out for exhaust; (5) The liquid-filled battery cell treated in step (4) is sealed again with a forming nail, and then the capacity is divided. The specific steps of the capacity division include: (a) Perform a rest period of 8-12 minutes, then discharge at a constant current of 0.08-0.12C to 1.8-2.2V, followed by a second rest period of 8-12 minutes; (b) Charge at a constant current and constant voltage of 0.2-0.5C to 4-4.5V, then rest for 8-12 minutes three times, and then discharge at a constant current of 0.2-0.5C to a cut-off voltage of 2.2-2.8V; (c) After repeating step (b) 3-5 times, charge at a constant current of 0.3-0.35C for 40-80 minutes, followed by four rest periods of 8-12 minutes; (6) After the separation is completed, age at 40-60℃ for 48-72h, then pull out the nails for secondary exhaust.

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